Thinly
slice the onion and leek whites to approximately the same thickness,
and sweat them in a large rondeau with butter over low heat, being
careful not to caramelize the vegetables. Once the onions and
leeks are almost translucent, add the sliced garlic and cook until
tender. Deglaze with the Riesling and reduce until dry; add the
vermouth and cook until almost dry; then, add the chicken stock
and heavy cream and bring to a boil. Once the soup boils, turn
it down to a low simmer for 20 minutes.

While
the onion soup is cooking, Bring a pot of salted water to a boil
and blanch the spring onion tops for one minute, then add the
parsley and cook for an additional 30 seconds. Remove the onion
tops and parsley and plunge them in an ice bath until they are
no longer hot. Squeeze out any excess liquid and blend until smooth.

After
the soup has simmered for 20 minutes, remove it from the heat.
Working in small batches, put equal amounts of the liquid and
the onions in the blender and blend until smooth. Pass it through
a fine strainer.

To
serve, heat up the soup with 4 tablespoons of the parsley/onion
puree and mix them with an immersion blender or whisk. At the
restaurant, we garnish the soup with a Maine crab flan and crab
salad, but at home, something as simple as some picked crabmeat
and sliced chives dressed with lemon juice would be perfect.